1. Field of the Invention
The present invention relates to an imaging device for taking images of a subject.
2. Description of the Related Art
In recent years, imaging elements having up to ten million pixels have been employed for digital still cameras of which primary usage is taking still images, and also imaging elements having several million pixels have been employed for movie cameras of which primary usage is taking moving images. With the above-described usages, in general, taking images has been performed with the high number of pixels in the event of taking high-definition images required for high resolution, and with the low number of pixels in the event of low resolution. In this process, in the event of taking high-definition images, generally all pixel signals have been read out from the imaging elements, and in the event of taking low-resolution images, pixel-signal thinning-out readout and readout for performing both pixel-signal thinning-out and addition, have been performed either to prevent the camera from excessive battery consumption, or to increase the number of shots. Examples of the above-described conventional arrangements include Japanese Patent Laid-Open No. 9-247689 and Japanese Patent Laid-Open No. 2001-36920.
With the arrangement disclosed in Japanese Patent Laid-Open No. 9-247689 (FIG. 3 in the Publication), readout addition is performed by thinning out the same color in increments of 4×4 pixels.
With the arrangement disclosed in Japanese Patent Laid-Open No. 2001-36920 (FIG. 1 in the Publication), a plurality of pixel signals are added, with 4×4 pixels making up one group, such that spatial color array of each color is the same before and after addition.
With Japanese Patent Laid-Open No. 9-247689, the number of valid pixels used in 4×4 pixels is few. Recent imaging elements have reduced unit-pixel size owing to high pixelation, and insufficient sensitivity is becoming a more prominent issue. With digital still cameras, while insufficient sensitivity in shooting of a dark subject can be compensated for with flash emission, taking moving images generates a great amount of noise since an expensive and heavy light source cannot be used. Furthermore, moiré occurs due to deterioration of image sampling frequency owing to pixel-signal thinning-out, resulting in marked deterioration of image quality.
With Japanese Patent Laid-Open No. 9-247689, while sensitivity can be improved by increasing the number of pixel signals to be added within one group, a problem is to provide pixel signals, which are not used (discarded). Moreover, while a plurality of pixel signals are added within one group such that spatial color array of each color becomes the same before and after addition, a problem is that a small amount of moiré can be observed under magnification.
As described above, with the conventional techniques, there are problems wherein improvement of sensitivity is insufficient due to thinning out of pixel signals, and also, moiré occurs even though the spatial color array is the same.